Patent Document No. 1 discloses a water current power generator comprising a horizontal-axis water turbine forming a float, a speed increasing gear train-power generator assembly engaging one end of the horizontal-axis water turbine, a speed increasing gear train-power generator assembly engaging the other end of the horizontal-axis water turbine, and a pair of arm members, wherein each arm member is fixed to a casing of one of the speed increasing gear train-power generator assemblies at one end and supported rotatably around a horizontal axis by a fixed structure above a water current at the other end, and the horizontal-axis water turbine floats on a river water surface.